DEVELOPMENT OF PLANTS 469 



presence of essential oils and resins in the roots, stems, leaves or 

 especially in the fruits which usually contain oil cavities between 

 the ribs of the ovary. These substances are the sources of the 

 peculiar odors that make easy the recognition of these plants. 

 These oils give the commercial value to several fruits, as in the 

 caraway, parsley, fennel, anise, coriander. Several species con- 

 tain very poisonous alkaloids, as the water hemlock {Ciciita), 

 among the most poisonous of our native plants, and the hemlock 

 (Conium) which perhaps furnished the potion drunk by Socrates. 

 Several valuable food plants, as the carrot, parsnip, celery, par- 

 sley, are cultivated species of the family. 



Series b. Sympetalae. 



149. General Characteristics. — This group contains the most 

 common and abundant of our flowering plants, approximating 

 42,000 species, and ranks as the most specialized of the angio- 

 sperms. The variations of these plants have been very success- 

 ful, especially to be noticed are the development of underground 

 stems, special types of flower structures and the massing of the 

 flowers in dense inflorescences. As a result of these advantages, 

 they exceed all other groups in the number of individuals, though 

 they comprise fewer orders as a consequence of the striking 

 uniformity in the floral structure. 



While a few of the simpler members of this group have dis- 

 tinct petals, the crowding of the organs on the receptacle has 

 resulted, in nearly all the forms, in the sympetalous type of 

 corolla, in the cyclic arrangement of the parts, and in the reduc- 

 tion in the number of stamens, so that each whorl does not exceed 

 the number of petals, and more frequently one whorl of stamens 

 is partly or entirely suppressed. The pistils are usually less 

 numerous than the petals. The flowers range from regular 

 hypogynous forms to epigynous and irregular types through the 

 same series of variations, as noted in the Choripetalae. The 

 Sympetalae are the most recently evolved of the Angiospermae, 

 as is apparent from their uniformity of structure and they 

 appear to be adapted to temperate and northern conditions where 

 they have preempted the open country and flourished exceedingly. 



